"Rosetta is a unique mission, unique by its scientific goal," Dordain said. "Understanding our origins is certainly the best way to understand our future."

On its Twitter page, the Rosetta mission said "Hello, comet!" in the languages of the agency's 20 nations.

Experts follow the flight path of the robotic space probe 'Rosetta' in the ESA control centre in Darmstadt, Germany. (AAP) ()

"It's a historic meeting and a great first in world science, which the global space community has been awaiting for a decade," Jean-Yves Le Gall, president of France's National Centre for Space Research (CNES), a major contributor to the project.

ESA showed a close-up picture of a gnarled, greyish object, comprising two lobes joined by a neck. The surface is pucked by what seems to be impact marks.

"Our first clear views of the comet have given us plenty to think about," project scientist Matt Taylor said.

"Is this double-lobed structure built from two separate comets that came together in the Solar System's history, or is it one comet that has eroded dramatically and asymmetrically over time?"

Launched in March 2004, Rosetta had to make four flybys of Mars and Earth, using their gravitational force as a slingshot to build up speed to catch up with its prey.